1. Field of the Invention
This invention relates to a joint structure for upper and lower casings of a two-part housing within which a tape medium or disk medium is enclosed.
2. Prior Art
Most of existing tape cartridge housings or cartridges have a housing or enclosure formed by upper and lower half casings tightened together along the mating faces of their sidewalls to provide a space in which a tape medium such as magnetic tape is accommodated. With a cartridge of the type described, the upper and lower casings are tightened together using tapping bosses formed at the four corners (or somewhere else, as the case may be). For example, Japanese Utility Model Application Kokoku No. 61-2805 introduces a cartridge in which the upper and lower halves of the housing have tapping bosses formed on opposing faces on the inner side and the two halves are joined together by setscrews inserted into throughholes of the bosses in one half casing and farther into corresponding tapping holes of the bosses in the other casing.
FIG. 1 gives outward views of a conventional cartridge and FIG. 2 shows relations between tapping bosses and the surrounding wall. In FIG. 1, (a) is a top view, (b) is a back view, (c) is a bottom view, and (d) is a left side view. The cartridge includes a housing which comprises an upper casing 100 and a lower casing 200 which are put together along the mating faces of their sidewalls and are joined with screws at five tapping parts 300, i.e., at the four corners and at a frontal, central point. FIG. 2 illustrates the structure of one of the tapping parts 300. A boss 110 extends downwardly from upper casing 100 toward lower casing 200, while a boss 220 extends upwardly from the lower casing toward the upper casing, and the two bosses are tightened together by means of a tapping screw 150.
The tendency toward smaller cartridges has necessitated reduction in the diameter of tapping bosses. Thickness of radiant ribs in the housing is limited to prevent shrinkage cavity at the time of molding. The lengths of the radiant ribs formed as reinforcements on the inner surfaces of the top and bottom walls that constitute the major planar surfaces of the upper and lower casings, are also restricted by the space requirement of the recording medium held within the housing. Consequently, the mechanical strength of the top and bottom walls is rather low. Under such circumstances, it has become increasingly difficult, when tightening the upper and lower casings together by screws, to join them by contacting only their tapping parts.
To be concrete, when the screw shown in FIG. 2(a) is tightened securely or to excess, bosses 110, 220 of the tapping part 300 fail to resist the force and are crushed at the mating ends as indicated in FIG. 2(b). As a consequence, the housing warps on the main planar surfaces toward their mechanically weak regions (in the case of lower casing 200, the regions around the holes through which drive shafts of a recorder are to be inserted, or the hatched regions, in FIG. 1(c), and in the case of upper casting 100, the corresponding regions). The sidewalls of the upper and lower casings are likewise in contact, but their contact area is large enough to resist crushing or deformation. The warp produces a gap as indicated in FIG. 1(b) or 1(d), deteriorating the configuration accuracy of the cartridge, marring the appearance, and impairing the dust-tightness of the housing.
The present invention is aimed at preventing the deformation of the major planar surfaces of the two-part housing of a cartridge and precluding the formation of any gap between the mating parts of its sidewalls.
The present invention solves the afore-described problems of the prior art by providing a cartridge including a housing which holds a tape medium or disk medium therein, said housing being composed of upper and lower casings which are joined with screws in bosses formed at the four corners, characterized in that the bosses in at least one of the upper and lower casings have ends with partially different heights each so that, when the upper and lower casings are joined, their bosses come in contact with one another before the sidewalls of the casings are mated.
The bosses are bosses for tapping and the portions of their ends directed to mechanically weak regions of the housing, or normally directed toward the center of the housing, are protruded.
With the construction according to the present invention, the force with which each pair of tapping bosses are fastened with a screw acts on and crushes the protruded portion of one tapping boss, but the restoring force is strong enough to resist warping of the major planar surfaces of the housing. Consequently, the major planar surfaces are leveled with no warp throughout, while the sidewalls of the upper and lower casings are uniformly mated, leaving no gap whatever in between.